1. Field of the Invention
The present invention relates generally to telecommunications systems and methods, particularly to system networks and methods for improved handovers within telecommunications systems, and, more particularly, to systems and methods for allocating cellular resources using signaling system commands.
2. Background and Objects of the Present Invention
The evolution of wireless communication over the past century, since Guglielmo Marconi's 1897 demonstration of radio's ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi's discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue to rise in the coming decades as well, as this wireless network interacts with and eventually overtakes the existing wireline networks.
As is well understood in the art, mobile phones have a limited range and communicate with respective base stations within cellular radio communication systems. Within such systems, a handover occurs when a mobile phone moves out of range of its existing base station (BS) contact within a given cell, i.e., the radiofrequency (RF) characteristics of the call connection deteriorate below a specified level or the RF characteristics of another BS in another, neighboring cell beneficially increases beyond a specific threshold relative to the current BS. Instead of allowing the call connection signal to deteriorate to noise level, the call connection is transferred or handed-over to another BS (and therefore another cell) to maintain the communication with the roving mobile subscriber. Handovers are also necessary in other situations to handle congestion and geographical problems, the details of which are irrelevant to the subject matter of the present invention.
Elaborate algorithms are utilized in determining whether or not to make a handover. These algorithms utilize measurements performed by the mobile station (MS) and the radio communication system or radio access network (RAN) within which the MS operates. For example, signal strength measurements on the active or operating cell(s) and neighboring cells are performed by the MS, which are known as Mobile Assisted Handover (MAHO), as well as signal strength measurements and quality supervision of the established connection via the active cell(s). Various neighboring cell information is needed for handover: the radio interface identification of the neighboring cells in the radio interface, e.g., by the frequency and code of the broadcast channel and radio-related parameter settings, such as minimum signal strength threshold levels; broadcast channel transmission level(s), etc. It should be understood that although a given identification should uniquely identify a particular cell, the same radio interface identification may be reused in different parts of a network. Such reuse must, of course, be planned so that a mobile station (user equipment) within a specific geographical area can only receive one specific radio interface identification within a given cell.
With reference now to FIG. 1, there is shown a portion of a radio access network, designated by the reference numeral 100, within which a given MS 110 operates. For simplicity, only the one MS 110 will be illustrated. It should, however, be understood that hundreds of discrete MSs would normally be operational within each cell within the RAN 100. The MS 110 is in contact with a BS 115 while roaming within cell 120. Cells 125, 130, 135, 140, 145 and 150 neighbor the active cell 120. With further reference to FIG. 1, the MS 110, currently operating within active cell 120, is moving toward neighboring cell 125 (as indicated by the arrow), the communications within which are controlled by another BS 155. It should be understood that BSs 115 and 155 preferably cover three-sector cells by use of antennas with pointing azimuths of 120 degrees. In other words, BS 115 covers each of cells 120, 140 and 145.
When MS 110 moves out of the range of BS 115, i.e., outside of cell 120, or more within the range of neighboring BS 155, i.e., within cell 125, a handover is initiated from BS 115 to BS 155, which then handles all of the wireless communications for that MS 110 while within communications contact. It should be understood, however, that another handover may shift control back to BS 115 should the MS 110 remain at the signal border between the base stations or geographical or meteorological characteristics come into play. In any event, a soft handover environment is envisioned where the user equipment, e.g., MS 110, communicates with various cells simultaneously, utilizing the macro-diversity characteristics of the soft handover technique, and dynamically establishing (and releasing) radio communication branches to support a continuous connection to the MS 110.
Inter-cell handovers are relatively straightforward when between cells under common control of a Radio Network Controller (RNC), which coordinates coverage over a group of cells.
Communications across discrete RNC coverage areas or between different Public Land Mobile Networks (PLMN), however, are more complicated, and much more identification information is required to effectuate cell-to-cell handovers across such boundaries. Not only cell identities but RNC and other controller information is required to effectively make such call transfers. For example, in an inter-RNC transfer, discussed in more detail in the Detailed Description portion of this specification, the signaling network address of the new RNC, along with relevant cell and neighboring cell data, is stored within the originating RNC to effectuate such handovers in conventional systems. The reason for the permanent storage of such elaborate routing information is to be prepared for all possible handovers.
There are, of course, problems associated with the storage of such detailed routing information. The first is size. Maintaining an elaborate list or database of all possible cellular transfer contingencies requires not only space but complicated updating procedures to keep the information within each RNC node updated with the most recent and correct cell information and RNC signaling network addresses throughout the entire system.
It is, therefore, an object of the present invention to simplify the mechanism for cell-to-cell transfers, particularly in the more complicated scenario of inter-RNC transfers.
It is also an object of the present invention to ameliorate or eliminate the complicated updating procedures needed in conventional systems.
It is a further object of the present invention to reduce the amount of information required to be stored within a given RNC in order to effectuate cell transfers.